1. Technical Field of Invention
The present invention relates to image forming apparatuses, image forming systems, and image forming methods for forming images by printing them on printing paper.
2. Related Technology
An image forming apparatus of this kind forms an image first on the front side of printing paper and then on the back side of the same printing paper. During a process in which an image is formed on the front side of the printing paper, the printing paper could shrink or expand, leading to a deviation between the image forming position on the front side of the printing paper and the image forming position on the back side of the printing paper.
To address this potential issue, Japanese Patent Application Publication, Tokukai, No. 2007-206667 (hereinafter, “Patent Document 1”) matches the image forming position on the front side of the printing paper with the image forming position on the back side of the printing paper through the following process. A reference mark is formed on the front side of the printing paper upon forming an image on the front side, and the position of the reference mark is detected twice, once before fixing and once after fixing. Subsequently, when an image is printed on the back side of the printing paper, the position and enlargement/reduction ratio are determined and specified for the image to be printed on the back side based on the deviation between the two detected positions of the reference mark, and the apparatus is set up accordingly. An image, enlarged/reduced (scaled up and/or scaled down) by the enlargement/reduction ratio, is then formed at the specified position on the back side of the printing paper.
Image quality could, however, suffer depending on the enlarging/reducing method being used. The quality of the image formed on the back side of the printing paper may fall if the image is enlarged/reduced when it is printed on the back side of the printing paper as in Patent Document 1.
Incidentally, a deviation between the image forming positions on the front and back sides of the printing paper is generally not a problem provided that the deviation is small in comparison to the image size. But, in cases where marks along which the printing paper is to be cut are formed on the front and back sides of the printing paper, a deviation in position of the cutting marks on the front and back sides of the printing paper is a problem: cutting the printing paper along those cutting marks formed on one side may leave uncut the cutting marks formed on the other side of the printing paper.
The present invention, conceived in view of these conventional problems, has an object to provide an image forming apparatus, an image forming system, and an image forming method that are capable of matching the positions of cutting marks and like indicators on the front and back sides of printing paper without sacrificing the quality of images formed on the printing paper.